La_1–xK_xFeO_3−δ: An Anion Intercalative Pseudocapacitive Electrode for Supercapacitor Application

Abstract

The green energy alternative to a fossil fuel-based economy can be provided only by coupling renewable energy solution solutions such as solar or wind energy plants with large-scale electrochemical energy storage devices. Enabling high-energy storage coupled with high-power delivery can be envisaged though high-capacitive pseudocapacitor electrodes. A pseudocapacitor electrode with multiple oxidation state accessibility can enable more than 1e – charge/transfer per molecule to facilitate superior energy storage. K-doped LaFeO3 (La1–x K x FeO3−δ) is presented here as an electrode having a high pseudocapacitance storage, equivalent to 1.32e – charge/transfer per molecule, resulting in a capacity equivalent of 662 F/g at 1 mV/s scan rate by introduction of a layered potential over the Fe-ion octahedral to utilize higher redox state energies (Fe4+→ Fe2+). La/K ordering in orthorhombic perovskite (La1–x K x FeO3−δ) made the Fe4+ oxidation state accessible, and a systematic shift in the redox energies of Fe4+/3+ and Fe3+/2+ redox couples was observed with K+ ion doping in the A site of the LaFeO3 perovskite, which resulted in a high faradic contribution to the capacitance, coupled with anionic intercalation of H2O/OH– in the host perovskite lattice. The surface capacitive and diffusion control contributions for capacitance are about 42 and 58%, respectively, at −0.6 V, with a scan rate of 1 mV/s. A high gravimetric capacitance, equivalent to 619, 347, 188, 121, and 65 F/g, respectively, at 1, 2, 3, 5, and 10 A/g constant current, was observed for the La0.5K0.5FeO3−δ electrode. Up to 88.9% capacitive retention and 97% Coulombic efficacy were obtained for continuous 5000 cycles of charge/discharge for the La0.5K0.5FeO3−δ electrode. The gravimetric capacitance values of ASCs (activated carbon//La0.5K0.5FeO3−δ) are 348, 290, 228, and 147 F/g at current densities of 1, 2, 3, and 5 A/g, respectively. A maximum specific power of ∼3594 W/kg was obtained when the specific energy reached ∼117 Wh/kg at 5 A/g of current density.

Perovskite La1−xKxCoO3−δ (0 ≤ x ≤ 0.5): a novel bifunctional OER/ORR electrocatalyst and supercapacitive charge storage electrode in a neutral Na2SO4 electrolyte

“…Thus after the determination of k 1 and k 2 , the current output can be quantified at specific potentials as the fraction of the current due to each of these contributions. 23,24,27 diffusion controlled redox-mediated (battery type) capacitance and La 0.5 K 0.5 CoO 3Àd has more surface controlled capacitance. Overall La 0.5 K 0.5 CoO 3Àd showed superior capacitance among all compositions.…”

“…5 CoO 3Àd sample presented in Fig. 2(a) contains C(1s), O(1s), La(3d), K(2s) (377.32 eV), Co(2p), and K(2p) (293.3 eV) 27,47 states. To investigate the Co oxidation state, core level XPS spectra of Co(2p) of the La 0 .…”

“…The value of b lies between 0.5 and 1; b = 0.5 stands for the diffusion controlled reaction or battery type behavior, b = 1 stands for the diffusion-controlled faradaic process, and the b value between 0.5 and 1.0 represents a hybrid chargestorage mechanism involving charge transfer with surface/ subsurface atoms. 23,24,27 Fig. S3(a) (ESI †) shows the kinetics of the charge storage mechanism of La 1Àx K x CoO 3Àd (0 r x r 0.5) in Na 2 SO 4 aqueous electrolytes analyzed from CV curves.…”

“…Perovskite (ABO 3 ) structured oxide materials have excellent properties because they can attain greater cation ordering as well as the ordering of oxygen ion vacancies resulting in fast mobility of oxygen ions (O 2À ) which improves both energy conversion (OER (oxygen Evolution Reaction) and ORR (oxygen Reduction Reaction)) processes. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] The e g electron points directly towards the surface O atom and plays an important role in O 2 2À /OH À exchange. The e g orbital filling was established as a determining parameter with optimal e g orbital occupancy close to 1 for superior OER/ORR activity and Ba 0.5 Sr 0.5 Co 0.8 -Fe 0.2 O 3Àd with nearly e 1 g configuration was invented as a superior OER catalyst.…”

“…Perovskite materials also reflect superior electrical and electronic properties that can be tuned systematically by cation substitutions at both A and B sites with different valence states and ionic sizes. [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] In this work, we present the synthesis, characterization, and electrochemical performance of the La 1Àx K x CoO 3Àd (0 r x r 0.5) perovskite in terms of supercapacitive charge storage in a neutral 0.5 M Na 2 SO 4 electrolyte and as an efficient OER/ORR electrocatalyst in a 1 M KOH electrolyte. The study also determines the role or tuning of oxygen vacancies by doping K + ions in LaCoO 3 resulting in novel electrocatalytic and energy conversion and storage properties.…”